In drop-feed irrigation the watering head is connected to the water source directly or indirectly with an irrigation pipeline laid in the vicinity of the ground surface, or is fastened to an irrigation pipeline that constitutes the part of an irrigation machine, e.g. a stationary, mobile in one place, towed or self-propelled irrigation unit. The watering head consists of two main parts, i.e. the body connected with the irrigation pipeline and the replaceable feeder unit mounted on the body. The irrigation water is delivered through the feeder unit onto the soil and/or plants at a pressure lower than 5 m, preferably 2 m H.sub.2 O water column.
Drop-feed irrigation has gained general acceptance during the last decade. Its main feature is that the water is delivered practically at a continuous rate, or intermittently with short intervals to the area to be irrigated, instead of in concentrated form occasionally during the growth season.
The water supply of the soil can be properly regulated with drop-feed irrigation and it is possible to provide optimal water quantity for the growth of the vegetation. A further advantage is that it is easy to automate and its servicing hardly requires manual labor.
A characteristic type of the water feeding heads suitable for drop feed irrigation is described in the French Pat. specification No. 2,185,349. The water is discharged through large-headed nails pressed into the irrigation hose that is provided with various gaps and/or holes. This type of water feeding head did not work in the practice, because the gaps or holes got clogged, while production of the heads was difficult and consequently expensive.
The drop-feed-type of watering device is described in the French Pat. No. 2,268,460. Here too the watering heads are inserted into the pipeline and are fastened with clamps. The watering heads consist of two parts, i.e. the body connected to the pipe and the replaceable feeder unit. The latter ones are provided with water outlet orifices along the mantle surface. The heads are complicated, material-intensive, the production is difficult and the orifices are sensitive to clogging.
A drop feed type head based on different principle is described in the French Pat. No. 2,281,719. The water passes through a large diameter orifice from the main conduit into the interior of the feeding head, where it is forced to travel a long distance. In spite of its conceptually correct and technically advanced construction the feeding head is not desirable, because its construction is even more complicated than those mentioned before; production of the head is more expensive and thus its general use cannot be reckoned with.
The drop-feed water-feeding head described in the French Pat. specification No. 2,229,347 is inserted into the irrigation pipeline as a pipe connecting adapter. One end of the adapter is provided with a square thread. The shape, depth, pitch and number of the threads determines the water quantity to be delivered. The otherwise correct basic idea here too results--just as in those mentioned before--in production operation and economic disadvantages.
It is more suited for the ploughland irrigation, but functions on the drop feed principle the water feeding device described in the French Pat. No. 2,175,616. This too is provided with a thread, and the water quantity is regulatd by the extent of screwingin. The water to be discharged flows in the grooves of the thread. Here too is the construction ingenious, but extremely complicated. Consequently it is expensive for the small-scale farms, while in the large-scale farms--owing to the need of continuous adjustment of the feeder pins--it is impractical, because it requires a large amount of manual labor.
Most drop-feed water-feeding devices deliver 1.5 to 5.0 liters of water per hour. In light of this the orifices are of narrow cross section; generally the diameter is between 0.25 and 0.60 mm. Owing to the very narrow hole cross sections, the risk of clogging is prevented by subjecting the irrigation water to filtering and in certain cases to other purification treatments.
In principle the irrigation water does not require intensive purification and the irrigation with purified water becomes more expensive with the investment and operation of the additional equipment. The irrigation of an orchard of 100 hectares land area in soil of average permeability in the temperate zone requires as much water as the drinking water supply of a settlement with 10,000 inhabitants. Consequently the basic cost of producing irrigation water is of vital importance.